Frequency tripled mode locked Nd:YAG pumped dye laser and single photon counting were used to study DNA folding. Fluorescence resonance energy transfer (FRET) experiments were carried out to investigate the interactions of high mobility group domain proteins with cisplatin-modified DNA. The DNA was tagged with pendant fluorescent donor and acceptor molecules. DNA fold angle was calculated based on fluorescence lifetimes versus donor-acceptor distance predicted by Forster theory.